Some television (TV) audio demodulator circuits receive a sound intermediate frequency (SIF) signal from a TV tuner circuit and convert the SIF signal into left and right audio signals. In addition, some TV audio demodulator circuits additionally provide a carrier mute functionality where the audio demodulator automatically mutes the audio or forces the audio to be mono in situations where one or both of the TV sound carriers in the SIF signal become too weak. Also, some TV audio demodulator circuits provide an automatic standard detection functionality whereby a signal broadcast using a TV audio standard can be automatically recognized and the appropriate demodulation and decoding circuitry can be engaged according to the detected standard.
However, under problematic broadcast conditions, such as when a broadcaster violates the specified parameters of the local broadcast standard, or under poor reception conditions, such as frequency selective fading, the carrier mute function and the automatic standard detection function can make the wrong decision. When the wrong decision is made, a TV may encounter several problems that may be disruptive to a viewer. First, the audio signals may switch back and forth between sound and silence while the sound is still acceptable. Second, the audio may be distorted due to a deep multipath null in the frequency spectrum. Third, a single over-modulated audio carrier may cause the system to attempt to send stereo signals to the speakers when only a mono signal exists. Hence, there is a need for an improved system and method of demodulating audio signals.